Top Notch Home Inspections – 301-487-3933


What is Radon ?


Radon is a colorless, odorless, tasteless radioactive gas produced by the decay of uranium and radium. Radon has a half-life of 3.8 days.

Radon causes lung cancer, and is the number one cause of lung cancer among non-smokers in the United States. The EPA recommends that all homes be tested for radon gas, as do I.

Should you test for radon?

All homes should be tested for radon. Simply put without a test you can’t know what the levels are in your home! Even if a home has a passive radon system does not mean there’s a low radon level. Even though homes with a basement are more susceptive to elevated levels does NOT mean a house on grade will be radon free. There are many factors that will determine radon levels. Primary among these is the presence and amount of source rock. A high radon level in a home is a potential liability. If you’re buying a home, it’s important to have it tested – ignoring the health effects, just think about the next owners.  Picture this: you buy a home and don’t have it tested for radon, you sell the home a year later, and the buyers have the home tested – then they find a high radon level, and ask you to pay for a mitigation system.  You might kick yourself for not testing the home when you bought it.

How does radon cause cancer?

The short short answer*- During the decay process, heavy Alpha  particles (2 protons & 2 neutrons), and radiation are released, if this happens while radon or its Decay Products are in the lungs, these partials can damage lung tissue-at the cellular level (DNA). When these damaged cells divide/reproduce the new cells are considered to be mutated. This growth of mutated cells is called cancer.

*Understand, the following longer, detailed, extended version, IS A SHORT explanation:

The atom

Radioactivity is simply the result of instability in the nuclei where there are too many or too few neutrons to satisfy the energy relationship within the nucleus of the radon atom.

Radioactive decay is the disintegration of the nuclei of the atom in a radioactive element. These disintegrations are usually accompanied by the release of pieces of the nucleus and sometimes by the release of energy in the form of gamma rays. As the nucleus of an atom releases these particles and energy, it changes into the nucleus of a different atom.

The radioactive decay chain for radon gas begins with uranium. Uranium decays through several intermediate steps to produce radium, which in turn produces radon. Radon then decays into other substances, Radon Decay Products or RDP’s, which are also radioactive. The process continues until non-radioactive lead is created.

Half-life is the time required for half the atoms of a radioactive element to decay. Example: If you have an amount of material with a half-life of 3.8 days, Radon, in 3.8 days you will have half as much. In another 3.8 days half of that half, or one quarter of the original amount. Every 3.8 days the remaining amount is halved. For all practical purposes, by the time ten half-life cycles have passed, so little is left one can call the remainder zero.

The half-life is important, because that time interval determines the time available for Radon and its decay products to be dispersed into the environment. The 3.8 day half-life is long enough to allow Radon gas to well disburse into the soil and into your house. On the other hand, the half-life’s of the Radon Decay Products are sufficiently short; if inhaled, they can cause significant radiation to reach the inner surface of the lungs before the decay products are removed by the natural cleansing process of the lungs.

Types of radiation





Uranium decay chain and RDP’s

Uranium 238—————(half-life-4.47 B years)

Radium 226—————-(half-life-1.82 years)

Radon 222—————–(half-life-3.8 days)        Alpha and gamma emitter

Polonium 218————-(half-life-3 minutes)         Alpha emitter

Lead 214——————-(half-life-27 minutes)        Beta and gamma emitter

Bismuth 214—————(half-life-19.7 minutes)        Beta and gamma emitter

Polonium 214————-(half-life-1.6 x 10-4 seconds)    Alpha and gamma emitter

lead 210——————–(half-life-19.4 years)        Beta and gamma emitter


How is radon measured and what do the results mean?

Radon is measured in pCi/L (picocurie/liter)

The action level recommended by the EPA is 4 pCi/L

The national average is 1.3

A curie is the radioactivity associated with 1 gram of radium
A picocurie is 1/trillionth (a millionth of a millionth) of a curie

A picocurie of Radon refers to an amount of radioactivity that emits 2.22 atomic disintegrations per minute.

Example: The amount of air that would fill a liter soda bottle with a Radon reading of 4 pCi/L would have 8.88 atomic disintegrations (decay) every minute.

Mitigation: The most common way of reducing radon in a home is sub-slab depressurization, which relieves the soil gas pressure below the home. Mitigation systems typically cost about $1,500.00 but there can be a wide range in prices.

Can radon levels continue to build?

As discussed the way radon affects us is through the atomic decay. Radon is produced and decays at a consistent, measurable rate – half-life. After about 12 hours radon levels are said to have reached equilibrium. This means the level of radon entering the house is equal to the level of radon decay.  Radon levels do fluctuate, from day to night, during the different seasons, weather and other factors can also affect radon levels in a home. This is why your test results will indicate average levels. Seasonally, winter generally has the highest levels; one reason is the furnace is in use and using air in the combustion process and the house is closed. This will create a vacuum effect in the house (nothing you or I would notice). This stack (vacuum) effect pulls the radon up through the foundation.


Can radon levels Fluctuate?  

Yes! they can vary dramatically. The average on this chart (an actual test courtesy of James Keton ) varies by about 2-3 pCi/L. The high 48 Hour average is around 6 pCi/L. and the low average is around 3 pCi/L.

Does this invalidate a test? The EPA recommends a long term test for readings of under 10 pCi/L. For readings over 10 pCi/L. it is highly unlikely a test will result in an average under 4 pCi/L.

This is an actual print out of a radon test done over a 2 week period.

The points represent hourly readings – observe the variations in the hourly readings. 

Photo Courtesy James Katen

How does radon get into you home?


Closed house conditions and why it is important !

US EPA and/or State Radon Testing Protocols must be followed for valid test results:

Closed building conditions and air circulation. Since radon and its decay products can fluctuate from hour to hour and season to season the following recommendations for closed building conditions and air circulation were developed by the EPA to provide standardized conditions under which a short-term radon survey is to be performed in order to reduce the variation the radon levels in foresaid property. These conditions will tend to maximize the radon measurement in order to determine if a dwelling has the potential to have an elevated radon level. All exterior windows and doors must be kept closed. All doors to and from the lowest livable area must be kept closed except for normal momentary entering and exiting during testing. Heating, air conditioning, dryers, range hoods, bathroom fans and attic ventilators can be operated normally. However any heating, air conditioning or ventilating equipment that has a built in outdoor air supply that is manually controlled, shall be turned off or the inlet closed. Fireplaces or wood stoves shall not be operated unless they are a primary heat source. Whole house fans shall not be operated. Window fans shall be removed and sealed shut. These test conditions must be initiated 12 hours prior to start of the radon device being placed and must be maintained for the duration of the testing not exceeding 4 days.

  • Keep all windows closed.
  • Keep all exterior doors closed except for normal entry and exit.
  • Leave all heating or A/C thermostats at normal settings.
  • Do not operate whole-house fans, fireplaces or wood stoves.
  • Do not touch or move the detectors.  Tampering with the detectors or refusal to follow these protocols will void the test.

This is a mouthful but I hope it helps put radon in perspective.

Anyone with questions about this test should contact Dan at Top Notch Home Inspections – 301-487-3933. Thank-you!


  1. Randi on April 4, 2019 at 3:36 am

    Simply dropped in from social media. Discovered this post really interesting.

  2. Christen on April 3, 2019 at 12:45 pm

    Wonderful topic, I ‘d like to learn more about it in the future.

    • topnotch on April 3, 2019 at 3:27 pm

      Thanks so much. I’ve been out with heath issues (surgery) but I am getting back into it. There is more I have to say on this and many other subjects.

  3. Lashay on March 17, 2019 at 12:21 pm

    Thanks for such an interesting post. I really took pleasure in reading this.

  4. Katherin on March 14, 2019 at 6:07 am

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